I have a lounge with two ceiling lights and there are four wires to one of them. I am trying to fit a new light fitting but seem to have mixed up the cables as the lighting circuit does not work. I have checked fuse but OK. I think the problem may be with the switched live but cannot find the right combination of wires. Can anyone help please?

you will need some kind of tester to determine the switch line, eg multimeter and the knowledge to use it safely, if not get some help, please.
As it says at the top look in 'projects' for diagrams to help.
Basically your 4 cables are :
1] in from mains or previous light in another room.
1] out to next room.
3] switch feed & return line.
4]loop to other light in same room.
you don't mention colours but will assume old red/blacks,
as you may know one of the blacks is switched line back to fitting and should have been marked with red sleeving/tape, this needs to be found by testing from black at switch to each black in turn at light to locate correct one with POWER OFF to the circuit!
Once found & marked, you must then find out which cable goes to second lounge light as it is connected to the same pair as go to the lampholder of first light.
This may not be easy and again you may need professional help.
regards Sparx